The present invention relates to a start control device including a compression self-ignition engine for combusting a fuel injected into a cylinder by a self-ignition. The start control device automatically stops the engine when a predetermined automatic stop condition is satisfied, and when a predetermined restart condition is satisfied, restarts the engine by injecting the fuel into a compression-stroke-in-stop cylinder that is on a compression stroke while the engine is stopped, while applying a torque to the engine by using a starter motor.
In recent years, compression self-ignition engines represented by a diesel engine have been widely familiarized as in-vehicle engines for reasons of their generally excellent thermal efficiency and less discharge amount of CO2 compared to spark-ignition engines, such as gasoline engines.
For larger reduction of CO2 in such compression self-ignition engines, it is effective to adopt the art of a so called idle stop control of automatically stopping the engine under, for example, an idle drive, and then automatically restarting the engine when, for example, a starting operation of the vehicle is performed, and various studies relating to this have been performed.
For example, JP2009-062960A (paragraph [0048]) discloses a control device of a diesel engine for automatically stopping the diesel engine when a predetermined automatic stop condition is satisfied, and when a predetermined restart condition is satisfied, restarting the diesel engine by injecting a fuel while applying a torque to the engine by driving a starter motor. Further, it is disclosed that a cylinder into which the fuel is injected first is changeably set based on a stop position of a piston of a cylinder that is on a compression stroke while an engine is stopped, in other words, when the engine stop is completed (compression-stroke-in-stop cylinder).
Further specifically, when the diesel engine is automatically stopped, a position of the piston of the compression-stroke-in-stop cylinder that is on the compression stroke at that time is determined, and it is determined whether the piston position is within a predetermined reference stop position range set relatively on a bottom dead center (BDC) side. When the piston position is within the reference stop position range, in restarting the engine, the fuel is injected into the compression-stroke-in-stop cylinder first, and on the other hand, when the piston position is on a top dead center (TDC) side of the reference stop position range, when the engine overall passes the TDC for the first time in the restart and an intake-stroke-in-stop cylinder (cylinder on intake stroke while the engine is stopped) reaches the compression stroke, the fuel is injected into the intake-stroke-in-stop cylinder.
According to such a configuration, when the piston of the compression-stroke-in-stop cylinder is within the reference stop position range, by injecting the fuel into the compression-stroke-in-stop cylinder, the fuel can surely self-ignite and the engine can promptly be restarted in a comparatively short time period (referred to as “the first compression start” for convenience). On the other hand, when the piston of the compression-stroke-in-stop cylinder is located on the TDC side of the reference stop position range, because a compression stroke amount (compression margin) is less and a temperature of air inside the cylinder does not rise sufficiently, a misfire may occur even when the fuel is not injected into the compression-stroke-in-stop cylinder. Therefore, in such a case, the fuel is injected into the intake-stroke-in-stop cylinder and not the compression-stroke-in-stop cylinder, and thereby, the air inside the cylinder is sufficiently compressed and the fuel can surely self-ignite (referred to as “the second compression start” for convenience).
As described above, conventionally, when restarting the engine, it is determined whether the piston of the compression-stroke-in-stop cylinder is stopped within the reference stop position range, and when the piston is stopped therein, the fuel is injected into the compression-stroke-in-stop cylinder and the engine is promptly restarted by the first compression start. Here, to better ensure a prompt engine restart by increasing the potential of the first compression start, it is desirable to enlarge the reference stop position range toward the TDC as much as possible. However, when the piston is stopped relatively on the TDC side, because a compression stroke amount becomes less than when the piston is stopped relatively on the BDC side, a temperature inside the cylinder when being compressed to the TDC (referred to as “the TDC temperature” for convenience) accordingly becomes insufficient and the fuel may not ignite. Therefore, in the conventional first compression start, a problem arises in that there is no choice but to limit the reference stop position range to a range close to the BDC, which is problematic because the reference stop position range is relatively narrow.